Using an orbiting camera designed to block the light from the sun and stars, an
international team of solar physicists has been able for the first time to
directly image clouds of electrons surrounding Earth that travel from the sun
during periods of solar flare activity.

These electron clouds, a part of the solar atmosphere that extends millions of
miles from the sun, cause geomagnetic storms that can disrupt communications
satellites, expose high-flying aircraft to excess radiation and even damage
ground-based power-generating facilities.

The images taken by this new camera, which will be discussed at a scientific
session and news conference at the fall meeting in San Francisco of the American Geophysical Union, should allow space weather forecasters to substantially
improve their predictions of geomagnetic storms.

“Until now, we didn’t have a good way to view the clouds of electrons that pass
Earth from coronal mass ejections,” said Bernard V. Jackson, a solar physicist
at the University of California, San Diego. “We are living inside the solar
atmosphere, but up until now had no way to view it, so space forecasters
couldn’t be certain whether an ejection from the sun would affect the Earth one
to five days later or harmlessly pass us by. Now that we can see these clouds as they travel through space outward from the sun, we can map their trajectories.”

The orbiting camera, known as the Solar Mass Ejection Imager, was built by
scientists and engineers at UCSD, the Air Force Research Laboratory, University
of Birmingham in the United Kingdom, Boston College and Boston University. The
instrument was launched in January by the Air Force and has provided the team of scientists with numerous images of coronal mass ejections, which can be seen in
the images because of the faint scattering of sunlight from the clouds of

To the surprise of the scientists, the images also revealed the existence of
high-altitude auroras, extending more than 500 miles above the Earth’s surface.
Such auroras had previously been reported by space-shuttle astronauts, but their observations were questioned because air molecules were not thought to exist in
sufficient quantity at that altitude to produce such light displays.

Bright auroras seen from the surface of our planet in the high northern and
southern latitudes are caused by pulses of charged particles, mostly electrons,
from the sun that overload the Earth’s lower radiation belt and are discharged
into the atmosphere, colliding with air molecules in the atmosphere in
shimmering displays of colorful light known as the northern (or southern)
lights. Auroras typically extend from 60 miles above Earth’s surface to several
hundred miles. But at 500 miles above the Earth’s surface, the density of air
molecules is not enough to permit auroras — or so scientists have long

“It’s a mystery,” said Jackson of UCSD’s Center for Astrophysics and Space
Sciences. “This is far higher than anyone had ever expected. It may be that
nitrogen from the ionosphere is ejected into the higher altitudes during a
coronal mass ejection.”

The auroras were first noted by Andrew Buffington, another UCSD solar physicist, while combing through data taken by the Solar Mass Ejection Imager. In a series
of image frames taken four seconds apart during a coronal mass ejection in late
May, Buffington detected a bright source of light, 100 times brighter than the
scattering of sunlight from the electrons. Similar sequences were seen during
subsequent mass ejections by Buffington and Boston College scientists Don Mizuno and Dave Webb.

“We’ve observed high-altitude auroras during all of the coronal mass ejection
events that engulfed Earth since the instrument became operational,” says
Jackson. “In fact, the last big event in late October had a lot of auroras
associated with it. But we still don’t understand the process that is causing

He said researchers at the Air Force Research Laboratory are presently studying
the data to come up with some possible explanations. The project was financed by the U.S. Air Force, National Aeronautics and Space Administration, National
Science Foundation and the University of Birmingham.


[Image 1: (237KB)]
Photo sequence from top left to bottom right showing high energy electrons in
yellow and red approaching Earth. Sun is at the center of the photo.

[Image 2: (64KB)]
High altitude aurora is seen as bright light in the center of these sequential
images taken two minutes apart.

[Movie: (1.9MB)]
Video showing clouds of high-energy electrons in red and yellow as they approach

Earth. Sun is at center of picture. Gaps in picture represent high-altitude